Metal-oxide-semiconductor transistor device having a drain side dummy contact

ABSTRACT

A MOS transistor device includes a substrate including a gate formed thereon, and a spacer being formed on a sidewall of the gate; a source region and a drain region formed in the substrate; and at least a first dummy contact formed above the substrate on a drain side of the gate. More important, the first dummy contact is formed apart from a surface of the substrate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a metal-oxide-semiconductor (hereinafterabbreviated as MOS) transistor device, and more particularly, to a highvoltage metal-oxide-semiconductor (herein after abbreviated as HV MOS)transistor device.

2. Description of the Prior Art

Integrated circuits (IC) technologies not only progressed in featuresize and integration density but also in integrating various MOStransistor devices into one chip (or die). For example, insystem-on-chip (SOC) technologies, different types of microelectronicdevices such as logic devices, analog devices, memory arrays, and highvoltage devices may be integrated into one semiconductor wafer aimed forimproving circuit performance, reliability, manufacturing cycle time,cost, device speed, and other advantages. In other exemplar, HV MOStransistor devices and mixed-signal circuit may be combined together forvarious applications.

HV MOS transistor device typically uses well implants to create thesource, drain and drift regions while the essential feature of HV MOStransistor device is the lateral-diffused drift region with low dopantconcentration and large area that is used to alleviate the high voltagebetween the drain and the source. For working in the high voltagecondition, it is known that the breakdown voltage (BVD) and reliabilityare key factors for the HV MOS transistor device, and thus improvementsto BVD and device reliability are always in need.

SUMMARY OF THE INVENTION

According to the claimed invention, a MOS transistor device is provided.The MOS transistor device includes a substrate including a gate formedthereon, and a spacer being formed on a sidewall of the gate; a sourceregion and a drain region formed in the substrate; and at least a firstdummy contact formed above the substrate on a drain side of the gate.More important, the first dummy contact is spaced apart from a surfaceof the substrate.

According to the claimed invention, a method for manufacturing a MOStransistor device is provided. According to the method, a substrateincluding at least an isolation structure formed therein is provided.Next, a MOS transistor device is formed on the substrate, the MOStransistor device includes a gate, a source region, a drain region and aspacer. After forming the MOS transistor device, at least a first dummycontact is formed on a drain side of the gate. The first dummy contactis spaced apart from a surface of the substrate.

According to the MOS transistor device and manufacturing method thereofprovided by the present invention, the first dummy contact is formed onthe drain side of the gate. More important, the first dummy contact isformed above and spaced apart from the surface of the substrate. Thatis, the first dummy contact never contacts the surface of the substrate.It is observed that by positioning the first dummy contact on the drainside of the gate, electrical fields are adjusted and pushed away fromthe gate. Accordingly, linear drain current (Idl) degradation isreduced, and both BVD and reliability are improved.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-3 are schematic drawings illustrating a method for manufacturinga HV MOS transistor device provided by a first preferred embodiment ofthe present invention, wherein

FIG. 2 is a schematic drawing in a step subsequent to FIG. 1, and FIG. 3is a schematic drawing in a step subsequent to FIG. 2.

FIG. 4 is a schematic drawing illustration a comparison between the HVMOS transistor device provided by the preferred embodiment and aconventional HV MOS transistor device.

FIGS. 3 and 5-6 are schematic drawings illustrating a method formanufacturing a HV MOS transistor device provided by a second preferredembodiment of the present invention, wherein

FIG. 6 is a schematic drawing in a step subsequent to FIG. 5, and FIG. 3is a schematic drawing in a step subsequent to FIG. 6.

FIGS. 3 and 7-8 are schematic drawings illustrating a method formanufacturing a HV MOS transistor device provided by a third preferredembodiment of the present invention, wherein

FIG. 8 is a schematic drawing in a step subsequent to FIG. 7; and FIG. 3is a schematic drawing in a step subsequent to FIG. 8.

FIG. 9 is a schematic drawing illustrating a modification to the firstto third preferred embodiments of the present invention.

FIG. 10 is a schematic drawing illustrating a fourth preferredembodiment of the present invention.

DETAILED DESCRIPTION

Please refer to FIGS. 1-3, which are schematic drawings illustrating amethod for manufacturing a HV MOS transistor device provided by a firstpreferred embodiment of the present invention. As shown in FIG. 1, asubstrate 102, such as a silicon substrate, is provided. A deep well 104is formed in the substrate 102. The deep well 104 includes a firstconductivity type while the substrate 102 includes a second conductivitytype. The first conductivity type and the second conductivity type arecomplementary to each other. In the preferred embodiment, the firstconductivity type is an n type and the second conductivity type is a ptype. However those skilled in the art should easily realize that it canbe vice versa. Accordingly, the preferred embodiment provides ap-substrate 102 and an n-deep well 104. Then, a pad oxide layer (notshown) and a patterned hard mask (not shown) for defining placement andsize of a plurality of isolation structures are sequentially formed onthe substrate 102. Next, the pad oxide layer and substrate 102 areetched with the patterned hard mask serving as an etching mask.Consequently, a plurality of shallow trenches (not shown) are formed inthe substrate 102.

Please still refer to FIG. 1. After forming the shallow trenches, aninsulating material is formed to fill up the shallow trenches andfollowed by performing a planarization process. Consequently,superfluous insulating material and the pad oxide layer are removed anda plurality of STIs are formed in the substrate 102. Additionally,surfaces of the STIs are coplanar with a surface 102S of the substrate102 in the preferred embodiment, but not limited to this. Some of theSTIs are used to provide electrical isolation between the devices and atleast one STI is formed in the deep well 104 as shown in FIG. 1. Itshould be noted that though the STI are used as an isolation structure110 in the preferred embodiment, those skilled in the art would easilyrealized that field oxide (FOX) structures can be adopted as theisolation structure in a modification to the preferred embodiment.

Please still refer to FIG. 1. After forming the isolations structure110, a well region 120 is formed in the substrate 102. The well region120 includes the second conductivity type and serves as a p-base regionin the preferred embodiment. Next, a gate dielectric layer 132 and agate conductive layer 134 such as a polysilicon layer are sequentiallyformed on the substrate 102. The gate conductive layer 134 and the gatedielectric layer 132 are then patterned, and thus a gate 130 is formedon the substrate 102 as shown in FIG. 1. A spacer 136 is subsequentlyformed on sidewalls of the gate 130. It is noteworthy that the gate 130covers a portion of the isolation structure 110 in the preferredembodiment. Next, a drain region 140D, a source region 140S, and a dopedregion 142 are formed in the substrate 102. As shown in FIG. 1, thedrain region 140D is formed in the deep well 104 while the source region140S and the doped region 142 are formed in the well region 120.Furthermore, the source region 140S and the doped region 142 abut uponeach other. According to the preferred embodiment, the drain region 140Dand the source region 140S both include the first conductivity type andthe doped region 142 includes the second conductivity type. Therefore,the preferred embodiment provides an n-drain region 140D, an n-sourceregion 140S, and a p-doped region 142. More important, the drain region140D is spaced apart from the gate 130 by the isolation structure 110 asshown in FIG. 1. Then, an insulating material 150 is formed on thesubstrate 102. The insulating material 150 serves as an interlayerdielectric (ILD) layer according to the preferred embodiment.

Please refer to FIG. 2. Next, an etching process is performed to etchthe insulating material 150 and thus to simultaneously form a gatecontact hole 160, a source contact hole 162, a drain contact hole 164,and a dummy contact hole 166 in the insulating material 150. The gatecontact hole 160 is aligned with the gate 130, the source contact hole162 is aligned with the source region 140S and the drain contact hole164 is aligned with the drain region 140D. Furthermore, the dummycontact hole 166 is formed on a drain side of the gate 130, and isbetween the spacer 136 on the drain side and the drain region 140D. Morepreferably, the dummy contact hole 166 is formed next to the spacer 136as shown in FIG. 2. It is noteworthy that a width W_(d) of the dummycontact hole 166 is smaller than a width W_(G) of the gate contact hole160, a width W_(S) of the source contact hole 162 and a width W_(D) ofthe drain contact hole 164. The etching process stops when the sourceregion 140S, the gate conductive layer 134 and the drain region 140D arerespectively exposed at a bottom of the source contact hole 162, abottom of the gate contact hole 160 and a bottom of the drain contacthole 164. More important, because the width W_(d) of the dummy contacthole 166 is smaller than the widths W_(G)/W_(S)/W_(D) of the gatecontact hole 160, the source contact hole 162 and the drain contact hole164, the etching to the insulating material 150 in the dummy contacthole 166 is not completed when it is stopped. Therefore the insulatingmaterial 150 is exposed at a bottom of the dummy contact hole 166 asshown in FIG. 2. In other words, the isolation structure 110 is notexposed. Additionally, the widths W_(G)/W_(S)/W_(D) of the gate contacthole 160, the source contact hole 162 and the drain contact 164 can beidentical to or different from each other, depending on differentprocess or product requirements.

Please refer to FIG. 3. Then, a barrier layer is formed in the gatecontact hole 160, the source contact hole 162, the drain contact hole164 and the dummy contact hole 166 and following by filling up the gatecontact hole 160, the source contact hole 162, the drain contact hole164 and the dummy contact hole 166 with a conductive material. Theconductive material includes, for example but not limited to, tungsten(W), aluminum (Al), copper (Cu). The superfluous conductive material isremoved by a planarization process and thus a gate contact 170, a sourcecontact 172, a drain contact 174 and a dummy contact 176 are obtained asshown in FIG. 3. Additionally, salicide layers can be formed beforeforming the insulating material 150. Or post-salicide process can beperformed to form salicide layers after forming the insulating material150 but before forming the contacts 170/172/174/176. As shown in FIG. 3,the gate contact 170 is electrically connected to the gate 130, thesource contact 172 is electrically connected to the source region 140S,and the drain region 174 is electrically connected to the drain region140D. More important, a wire 171 is formed to construct an electricalconnection between the gate contact 170 and the dummy contact 176.Therefore the gate contact 170 is not only electrically connected to thegate 130, but also to the dummy contact 176 by the wire 171.

Please refer to FIG. 3 again. Consequently, a MOS transistor device 100,more particularly, a HV MOS transistor device 100 is obtained. The HVMOS transistor device 100 includes the dummy contact 176 electricallyconnected to the gate contact 170. More important, the dummy contact 176is formed on the drain side of the gate 130 and above the surface 102Sof the substrate 102. Specifically, the dummy contact 176 is formedbetween the spacer 136 and the drain region 140D, preferably next to thespacer 136. And the dummy contact 176 is spaced apart from the surface102S of the substrate 102. It is noteworthy that since the preferredembodiment provides a HV MOS transistor device 100 of which the gate 130covers a portion the isolation structure 110, the dummy contact 176 ofthe preferred embodiment is particularly formed above and spaced apartfrom the isolation structure 110 by the insulating material 150 as shownin FIG. 3. And a distance “D” between a bottom of the dummy contact 176and the surface 102S of the substrate/a surface of the isolationstructure 110 is 4-7 times of a thickness “T” of the gate dielectriclayer 132.

Please refer to FIG. 4, which is a schematic drawing illustration acomparison between the HV MOS transistor device provided by thepreferred embodiment and a conventional HV MOS transistor device. Morespecifically, a conventional HV MOS transistor device is depicted on theleft side (L) of FIG. 4 and the MOS transistor device provided by thepreferred embodiment is depicted on the right side (R) of FIG. 4. Asshown in the left side (L) of FIG. 4, electric lines are gathered up ata bottom corner of the gate on the drain side in the conventional HV MOStransistor device. Different from the conventional HV MOS transistordevice, electric lines are gathered up at the bottom of the dummycontact 176 of the HV MOS transistor device 100 provided by thepreferred embodiment. It is therefore observed that electrical fieldsare pushed away from the gate 130 due to the placement of the dummycontact 176. Consequently, linear drain current (Idl) degradation isreduced from 9.88% to 8.76%, and BVD and reliability are improved.

Please refer to FIGS. 3 and 5-6, which are schematic drawingsillustrating a method for manufacturing a HV MOS transistor deviceprovided by a second preferred embodiment of the present invention. Itshould be noted that elements the same in the first and second preferredembodiments are designated by the same numerals and those details areomitted hereinafter in the interest of brevity. As shown in FIG. 5, thepreferred embodiment provides a substrate 102 including a deep well 104formed therein, and an isolation structure 110 is formed in thesubstrate 102, a well region 120 is then formed in the substrate 102.The deep well 104 includes a first conductivity type, and the substrate102 and the well region 120 include a second conductivity type. Thefirst conductivity type and the second conductivity type arecomplementary to each other. In the preferred embodiment, the firstconductivity type is an n type and the second conductivity type is a ptype. However those skilled in the art should easily realize that it canbe vice versa. Next, a gate 130 including a gate dielectric layer 132and a gate conductive layer 134 is formed on the substrate 102 andfollowed by forming a spacer 136 on its sidewall. A drain region 140Dincluding the first conductivity type, a source region 140S includingthe first conductivity type, and a doped region 142 including theconductivity type are formed in the substrate 102. As shown in FIG. 1,the drain region 140D is formed in the deep well 104 while the sourceregion 140S and the doped region 142 are formed in the well region 120.Then, an insulating material 150 serving as an ILD layer is formed onthe substrate 102.

Please still refer to FIG. 5. An etching process is then performed toetch the insulating material 150 and thus to form a gate contact hole160, a source contact hole 162 and a drain contact hole 164 in theinsulating material 150. The gate contact hole 160 is aligned with thegate 130, and the gate 130 is exposed at a bottom of the gate contacthole 160. The source contact hole 162 is aligned with the source region140S, and the source region 140S is exposed at a bottom of the sourcecontact hole 162. The drain contact hole 164 is aligned with the drainregion 140D, and the drain region 140D is exposed at a bottom of thedrain contact hole 164. The gate contact hole 160 includes a widthW_(G), the source contact hole 162 includes a width W_(S), and the draincontact hole 164 includes a width W_(D). In the preferred embodiment,the widths W_(G)/W_(S)/W_(D) of the gate contact hole 160, the sourcecontact hole 162 and the drain contact hole 164 are identical to eachother, but those skilled in the art would easily realize that thosewidths can be different from each other, depending on different processor product requirements.

Please refer to FIG. 6. After forming the gate contact hole 160, thesource contact hole 162, and the drain contact hole 164, another etchingprocess is performed to form a dummy contact hole 166 in the insulatingmaterial 150. In the preferred embodiment, the dummy contact hole 166includes a width W_(d), and the width W_(d) is substantially equal tothe widths W_(S)/W_(S)/W_(D) of the gate contact hole 160, the sourcecontact hole 162 and the drain contact hole 164. Furthermore, the dummycontact hole 166 is formed on a drain side of the gate 130, and isbetween the spacer 136 and the drain region 140D. More preferably, thedummy contact hole 166 is formed next to the spacer 136 as shown in FIG.6. It is noteworthy that the insulating material 150 is exposed at abottom of the dummy contact hole 166 as shown in FIG. 6. In other words,the isolation structure 110 is not exposed.

Please refer back to FIG. 3. After forming the dummy contact hole 166,the gate contact hole 160, the source contact hole 162, the draincontact hole 164 and the dummy contact hole 166 are filled up with aconductive material. And the superfluous conductive material is removedby a planarization process and thus a gate contact 170, a source contact172, a drain contact 174 and a dummy contact 176 are obtained as shownin FIG. 3. The gate contact 170 is electrically connected to the gate130, the source contact 172 is electrically connected to the sourceregion 140S, and the drain region 174 is electrically connected to thedrain region 140D. More important, a wire 171 is formed to construct anelectrical connection between the gate contact 170 and the dummy contact176. Therefore the gate contact 170 is not only electrically connectedto the gate 130, but also to the dummy contact 176 by the wire 171. Itshould be easily understood that the placement of the dummy contact 176in the second preferred embodiment is the same with that in the firstpreferred embodiment except that the width W_(d) of the dummy contact176 is smaller than the widths W_(G)/W_(S)/W_(D) of the gate contact170, the source contact 172 and the drain contact 174 in the firstpreferred embodiment while the above mentioned widths W_(d), W_(G),W_(S), and W_(D) can be equal to each other in the second preferredembodiment.

Please refer to FIGS. 3 and 7-8, which are schematic drawingsillustrating a method for manufacturing a HV MOS transistor deviceprovided by a third preferred embodiment of the present invention. Itshould be noted that elements the same in the second and third preferredembodiments are designated by the same numerals. Furthermore, thosedetails are omitted hereinafter in the interest of brevity and only thedifferences between the second and third preferred embodiments aredetailed. The difference between the second and third preferredembodiment is: the dummy contact hole 166 is formed after forming thegate contact hole 160, the source contact hole 162 and the drain contacthole 164 as shown in FIGS. 5-6 of the second preferred embodiment, whilethe dummy contact hole 166 is formed before forming the gate contacthole 160, the source contact hole 162 and the drain contact hole 164 asshown in FIGS. 7-8 of the third preferred embodiment.

Please refer back to FIG. 3. After forming the gate contact hole 160,the source contact hole 162 and the drain contact hole 164, the dummycontact hole 166, the gate contact hole 160, the source contact hole162, the drain contact hole 164 are filled up with a conductivematerial. And the superfluous conductive material is removed by aplanarization process and thus a gate contact 170, a source contact 172,a drain contact 174 and a dummy contact 176 are obtained as shown inFIG. 3. The gate contact 170 is electrically connected to the gate 130,the source contact 172 is electrically connected to the source region140S, and the drain region 174 is electrically connected to the drainregion 140D. More important, a wire 171 is formed to construct anelectrical connection between the gate contact 170 and the dummy contact176. Therefore the gate contact 170 is not only electrically connectedto the gate 130, but also to the dummy contact 176 by the wire 171. Asmentioned above, the placement of the dummy contact 176 in the thirdpreferred embodiment is the same with that in the first preferredembodiment except that the width W_(d) of the dummy contact 176 issmaller than the widths W_(G)/W_(S)/W_(D) of the gate contact 170, thesource contact 172 and the drain contact 174 in the first preferredembodiment while the above mentioned widths W_(d), W_(G), W_(S), andW_(D) can be equal to each other in the third preferred embodiment.

As mentioned above, a MOS transistor device 100, more particularly, a HVMOS transistor device 100 is obtained. The HV MOS transistor device 100includes a dummy contact 176 electrically connected to the gate contact170. More important, the dummy contact 176 is formed on the drain sideof the gate 130 and above a surface 102S of the substrate 102. As shownin FIG. 3, the dummy contact 176 is spaced apart from the surface 102Sof the substrate 102. It is noteworthy that since the preferredembodiment provides a HV MOS transistor device 100 of which the gate 130covers a portion the isolation structure 110, the dummy contact 176 ofthe second and third preferred embodiments is particularly formed aboveand spaced apart from the isolation structure 110 by the insulatingmaterial as shown in FIG. 3. And a distance “D” between a bottom of thedummy contact 176 and the surface 102S of the substrate/a surface of theisolation structure 110 is 4-7 times of a thickness “T” of the gatedielectric layer 132.

Please refer to FIG. 9, which is a modification to the first to thirdpreferred embodiments provided by the present invention. It should benoted that elements the same in the first to third preferred embodimentsand the instant modification are designated by the same numerals.Furthermore, those details are omitted hereinafter in the interest ofbrevity and only the differences between the second and third preferredembodiments are detailed: According to the modification, the HV MOStransistor device 100 includes a plurality of dummy contacts 176 and176′ all simultaneously formed. As shown in FIG. 9, the dummy contacts176 and 176′ are all formed between the spacer 136 on the drain side andthe drain region 140D. At least one of the dummy contacts is formed nextto the spacer 136, and that dummy contact is emphasized by 176 whileother dummy contacts are designated by 176′ as shown in FIG. 9. Moreimportant, the dummy contacts 176/176′ are all spaced apart from thesurface 102S of the substrate 102. In the modification which adopts HVMOS technique, the dummy contacts 176/176′ are all formed above theisolation structure 110 and spaced apart from the isolation structure110 by the insulating material 150. Also a distance “D” between bottomsof the dummy contacts 176/176′ and the surface 102S of the substrate/asurface of the isolation structure 110 is 4-7 times of a thickness “T”of the gate dielectric layer 132. Furthermore, the dummy contacts176/176′ are all electrically connected to the gate contact 170.Additionally, an amount of the dummy contacts 176 can be adjusted to fitthe needs. It should be noted that the dummy contacts 176/176′ arearranged along a first direction D1 as shown in FIG. 9, however thoseskilled in the art would easily realize that the dummy contacts 176/176′can also be arranged in a second direction D2 that is perpendicular tothe first direction D1 as shown in FIG. 9.

It is noteworthy that the dummy contacts 176 and 176′ are all formedbetween the spacer 136 on the drain side and the drain region 140D.Accordingly, electric lines are gathered up at a bottom of the dummycontact 176′ proximal to the drain region 140D. It is therefore observedthat electrical fields are further pushed away from the gate 130 due tothe placement of the dummy contacts 176 and 176′. Consequently, lineardrain current degradation is reduced and both BVD and reliability areimproved.

Please refer to FIG. 10, which is a schematic drawing illustrating afourth preferred embodiment of the present invention. The preferredembodiment provides a substrate 202 including a deep well (not shown)formed therein, and a plurality of isolation structures 210 forproviding electrical isolation are formed in the substrate 202. Next, agate 230 including a gate dielectric layer 232 and a gate conductivelayer 234 is formed on the substrate 202 and followed by forming aspacer 236 on its sidewall. A drain region 240D and a source region 240Sincluding the first conductivity type are formed in the substrate 102.Then, an insulating material 250 serving as the ILD layer is formed onthe substrate 202.

Please still refer to FIG. 10. An etching process is then performed toform a gate contact hole (not shown), a source contact hole (not shown),a drain contact hole (not shown), and a dummy contact hole (not shown)in the insulating material 250. It should be easily realized that thedummy contact hole can be formed simultaneously with forming the gatecontact hole, the source contact hole and the drain contact hole asmentioned in the first preferred embodiment, it can be also formedbefore or after forming the gate contact hole, the source contact holeand the drain contact hole as respectively mentioned in the second andthird preferred embodiments. When the dummy contact hole is formedsimultaneously with forming the gate contact hole, the source contacthole and the drain contact hole, a width of the dummy contact hole issmaller than widths of the gate contact hole, the source contact holeand the drain contact hole. When dummy contact hole is formed before orafter forming the gate contact hole, the source contact hole and thedrain contact hole, the width of the dummy contact hole is equal to thewidths of the gate contact hole, the source contact hole and the draincontact hole, but not limited to this. Furthermore, the dummy contacthole is formed on a drain side of the gate 230, and is between thespacer 236 and the drain region 240D. More preferably, the dummy contacthole is formed next to the spacer 236. It is noteworthy that theinsulating material 250 is exposed at a bottom of the dummy contacthole. In other words, a surface 202S of the substrate 202 is notexposed.

Please still refer to FIG. 10. Next, the dummy contact hole, the gatecontact hole, the source contact hole, the drain contact hole and thedummy contact hole are filled up with a conductive material. And thesuperfluous conductive material is removed by a planarization processand thus a gate contact 270, a source contact 272, a drain contact 274and a dummy contact 276 are obtained as shown in FIG. 10. The gatecontact 270 is electrically connected to the gate 230, the sourcecontact 272 is electrically connected to the source region 240S, and thedrain region 274 is electrically connected to the drain region 240D.More important, a wire 271 is formed to construct an electricalconnection between the gate contact 270 and the dummy contact 276.Therefore the gate contact 270 is not only electrically connected to thegate 230, but also to the dummy contact 276 by the wire 271.

Accordingly, a MOS transistor device 200 is obtained. The MOS transistordevice 200 includes the dummy contact 276 electrically connected to thegate contact 270. More important, the dummy contact 276 is formed on thedrain side of the gate 230 and above a surface 202S of the substrate202. As shown in FIG. 10, the dummy contact 276 is spaced apart from thesurface 202S of the substrate 202 by the insulating material 250. And adistance “D” between a bottom of the dummy contact 276 and the surface202S of the substrate 202 is 4-7 times of a thickness “T” of the gatedielectric layer 232. Additionally, the MOS transistor device 200 caninclude a plurality of dummy contacts 276 formed between the drainregion 240D and the spacer 236 on the drain side and spaced apart fromthe surface 202S of the substrate 202 according to a modification to thepreferred embodiment.

According to the MOS transistor device or HV MOS transistor device andmanufacturing method thereof provided by the present invention, at leastone dummy contact is formed on the drain side of the gate. Moreimportant, the dummy contact is formed above and spaced apart from thesilicon surface of the substrate or from the insulating surface of theisolation structure. That is, the dummy contact never contacts thesurface of the substrate or the surface of the isolation structure. Itis observed that by positioning the dummy contact on the drain side ofthe gate, electrical fields are pushed away from the gate. Accordingly,linear drain current degradation is reduced and both BVD and reliabilityare improved.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A metal-oxide-semiconductor (MOS) devicecomprising: a substrate comprising a gate formed thereon, and a spacerbeing formed on sidewalls of the gate; a gate contact electricallyconnected to the gate; a source region and a drain region formed in thesubstrate; and at least a first dummy contact formed above the substrateon a drain side of the gate, the first dummy contact being formed apartfrom a surface of the substrate, and the first dummy contact beingelectrically connected to the gate contact.
 2. The MOS transistor deviceaccording to claim 1, further comprising a drain contact electricallyconnected to the drain region, and a source contact electricallyconnected to the source region.
 3. The MOS transistor device accordingto claim 2, wherein a width of the first dummy contact is smaller thanwidths of the gate contact, the drain contact and the source contact. 4.The MOS transistor device according to claim 2, wherein a width of thefirst dummy contact is substantially equal to widths of the gatecontact, the drain contact and the source contact.
 5. The MOS transistordevice according to claim 1, wherein the gate comprises a gatedielectric layer and a gate conductive layer.
 6. The MOS transistordevice according to claim 5, wherein a distance between the first dummycontact and the surface of the substrate is 4-7 times of a thickness ofthe gate dielectric layer.
 7. The MOS transistor device according toclaim 1, further comprising an isolation structure formed in thesubstrate, the drain region is spaced apart from the gate by theisolation structure, and the first dummy contact is formed above theisolation structure and spaced apart from a surface of the isolationstructure.
 8. The MOS transistor device according to claim 7, whereinthe first dummy contact is formed between the spacer and the drainregion.
 9. The MOS transistor device according to claim 8, wherein thefirst dummy contact is formed next to the spacer.
 10. The MOS transistordevice according to claim 1, wherein the first dummy contact comprisesconductive materials.
 11. The MOS transistor device according to claim1, further comprising at least a second dummy contact formed above thesubstrate on the drain side of the gate, and the second dummy contact isformed apart from the surface of the substrate.
 12. Ametal-oxide-semiconductor (MOS) device comprising: a substratecomprising a gate formed thereon, and a spacer being formed on sidewallsof the gate; an isolation structure formed in the substrate; a sourceregion and a drain region formed in the substrate, the drain regionbeing spaced apart from the gate by the isolation structure; and atleast a first dummy contact formed above the substrate and the isolationstructure on a drain side of the gate, the first dummy contact beingformed apart from a surface of the substrate and a surface of theisolation structure.